Study On Interfacial Strain Control Of Physical Properties In Perovskite Oxide Films

ABO3-type perovskite oxides have stimulated intensive scientific interest.due to their potential applications in photoelectric sensing,information storage,and chemical catalysis.Epitaxial strain imposed in complex oxide thin films by heteroepitaxy is recognized as a powerful tool for identifying new properties and exploring the vast potential of materials performance.Some kinds of thin films can respond to strain which are highly desired for the next-generation devices with requirements of smaller size and higher performance.In this paper,we indentify stain and the lattic distortion of the perovskite oxides,and measure the associated physical properties.The main contents and conclusions of this paper are displayed as follow:1.We present a systematic study of the effect of biaxial strain on the upconversion photoluminescence properties in lanthanide-doped ferroelectric thin films.Through control of the c/a ratios of BaTiO3:Er films,the luminescent intensity of the films can be effectively increased by over seven times.The observed phenomenon can be understood in terms of the variation in crystal field around Er3+ions induced by biaxial strain due to the lattice mismatch.Moreover,our results have bridged the identifications of lattice distortion and crystalline orientation through the light emission properties of lanthanide dopants.2.We demonstrate that a purely mechanical strain in a flexible mica substrate triggered by bending can be used to dramatically modify the photoluminescence response of BTO:Er epitaxial thin film in a stable and repeatable manner.In particular,because of the nature of mica,the film structure exhibits excellent antifatigue characteristics as well as high optical transparency in the range of 450-780 nm.This study offers new possibilities for developing allinorganic,reconfigurable,transparent and flexible light sources,photodetectors,and wearable sensors.3.Keeping the in-plane strain unchanged,we report that the magnetization of LaCoO3(LCO)films can be manipulated with crystallographic symmetry.The ultrathin LCO layers,constrained by the cubic substrate,have pseudotetragonal structure and small magnetization.Upon increasing the layer thickness,the monoclinic structure dominates the LCO film and maximizes its ferromagnetism.For the LCO films with a thickness beyond 35 unit cells,the symmetry relaxes gradually towards its rhombohedral bulk form,and meanwhile the magnetization reduces.These results highlight the importance of spin-lattice entanglement in a ferroelastic material and provide a concise way to maximize its functionality using symmetry engineering.4.We report a methodology for maintaining strong ferromagnetism inferroelastic LCO ultrathin layers with a thickness down to a single unit cell.We find that the magnetic and electronic states of LCO intimately link to the structural parameters of adjacent SrCuO2(SCO).As reducing the SCO thickness fewer than five-unit-cell,the oxygen coordination of SCO transforms from the planar-type to chain-type accompanied with a huge elongation along the growth direction.Consequently,the LCO ultrathin layers exhibit a distinct modulation of CoO6 octahedra with the significant shrink of bonding angle and elongation of bond length.This structural modulation reduces the crystal field splitting energy and promotes a higher spin state and long-range order of cobalt ions,resulting in an unexpected enhanced magnetization.Our results demonstrate a synthesize strategy for creating ultrathin ferromagnetic oxides by exploiting the atomically heterointerface engineering and spin-lattice entanglement in strongly correlated materials.